Mechanism for enabling full data bus utilization without increasing data granularity

ABSTRACT

A memory is disclosed comprising a first memory portion, a second memory portion, and an interface, wherein the memory portions are electrically isolated from each other and the interface is capable of receiving a row command and a column command in the time it takes to cycle the memory once. By interleaving access requests (comprising row commands and column commands) to the different portions of the memory, and by properly timing these access requests, it is possible to achieve full data bus utilization in the memory without increasing data granularity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/393,265, filed Feb. 26, 2009 for “MECHANISM FOR ENABLING FULL DATABUS UTILIZATION WITHOUT INCREASING DATA GRANULARITY,” which in turn is adivision of U.S. patent application Ser. No. 09/837,307 filed Apr. 17,2001, also entitled “MECHANISM FOR ENABLING FULL DATA BUS UTILIZATIONWITHOUT INCREASING DATA GRANULARITY,” now issued as U.S. Pat. No.7,500,075. Each of this prior applications is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to storage technology, and moreparticularly to a mechanism for enabling full data bus utilization in amemory without increasing data granularity.

BACKGROUND

Dynamic random access memories (DRAM's) are used as main memory in manyof today's computer systems. One of the factors that have led to thepopularity of the DRAM has been the DRAM's simple cell structure.Because each DRAM storage cell consists of just a single capacitor, itis possible to pack a very large number of storage cells into a verysmall amount of chip space. Consequently, with DRAM technology, it ispossible to manufacture very high-density, low cost memories.

With reference to FIG. 1, there is shown a functional diagram of atypical DRAM 100. As shown in FIG. 1, a DRAM 100 comprises a pluralityof memory cells 102 arranged in a plurality of rows and columns. Eachrow of memory cells 102 is coupled to one of the wordlines 104 of theDRAM 100, and each column of memory cells 102 is coupled to one of thebitlines 106. By specifying a wordline 104 and a bitline 106, aparticular memory cell 102 can be accessed.

To enable access to the various memory cells 102, there is provided arow decoder 112 and a column decoder 114. The row decoder 112 receives arow address on a set of address lines 116, and a row address strobe(RAS) signal on a control line 118, and in response to these signals,the row decoder 112 decodes the row address to select one of thewordlines 104 of the DRAM 100. The selection of one of the wordlines 104causes the data stored in all of the memory cells 102 coupled to thatwordline 104 to be loaded into the sense amplifiers (sense amps) 108.That data, or a portion thereof, may thereafter be placed onto the databus 110 (for a read operation).

What portion of the data in the sense amps 108 is actually placed ontothe data bus 110 in a read operation is determined by the column decoder114. More specifically, the column decoder 114 receives a column addresson the address lines 116, and a column address strobe (CAS) signal on acontrol line 120, and in response to these signals, the column decoder114 decodes the column address to select one or more of the bitlines 106of the DRAM 100. The number of bitlines 106 selected in response to asingle column address may differ from implementation to implementation,and is referred to as the base granularity of the DRAM 100. For example,if each column address causes sixty-four bitlines 106 to be selected,then the base granularity of the DRAM 100 is eight bytes. Defined inthis manner, the base granularity of the DRAM 100 refers to the amountof data that is read out of or written into the DRAM in response to eachcolumn address/CAS signal combination (i.e. each CAS or column command).

Once the appropriate bitlines 106 are selected, the data in the senseamps 108 associated with the selected bitlines 106 are loaded onto thedata bus 110. Data is thus read out of the DRAM 100. Data may be writteninto the DRAM 110 in a similar fashion. A point to note here is that ina typical DRAM, the address lines 116 are multiplexed. Thus, the samelines 116 are used to carry both the row and column addresses to the rowand column decoders 112, 114, respectively. That being the case, atypical memory access requires at least two steps: (1) sending a rowaddress on the address lines 116, and a RAS on the control line 118; and(2) sending a column address on the address lines 116, and a CAS on thecontrol line 120.

A timing diagram illustrating the various steps carried out duringtypical DRAM read cycles is shown in FIG. 2. As shown, to initiate aread cycle, a row address 208(1) is placed onto the address lines 116,and a RAS signal 202(1) is asserted on the RAS control line 118. Then, acolumn address 210(1) is sent onto the address lines 116, and a CASsignal 204(1) is asserted on the CAS control line 118. A short timethereafter, the data 206(1) stored at the locations indicated by the rowaddress 208(1) and the column address 210(1) appear on the data bus 110.Data is thus extracted from the DRAM 100. After the first set of data206(1) disappears from the data bus 110, a second read operation may beinitiated. Like the first read operation, the second read operationbegins with a row address 208(2) on the address lines 116, and a RASsignal 202(2) on the RAS control line 118. Then, a column address 210(2)is sent onto the address lines 116, and a CAS signal 204(2) is assertedon the CAS control line 118. A short time thereafter, the data 206(2)stored at the locations indicated by the row address 208(2) and thecolumn address 210(2) appear on the data bus 110. The second readoperation is thus completed. Additional successive reads may be carriedout in a similar fashion.

Notice from the timing diagram of FIG. 2 that, for individual readcycles, there is substantial idle time between successive data sets 206on the data bus 110. During this idle time, the data bus 110 is notutilized and no data is being transferred. The more idle time there is,the lower the utilization rate of the data bus 110, and the lower theutilization rate, the longer it will take for an external component(such as a CPU) to extract data from the DRAM 100. Since almost alloperations of a computer require the use of memory, the longer it takesto get data from a memory, the slower the performance of the overallcomputer system. Thus, low bus utilization can have a direct negativeimpact on the overall performance of a computer system.

To improve data bus utilization, several techniques have been developed.One such technique involves the use of a “burst” mode of operation.Basically, in burst mode, rather than implementing just one columnaccess for each RAS command, a plurality of column accesses are carriedout for each RAS command. This results in consecutively accessingmultiple sets of data from the same row of a DRAM 100. A timing diagramillustrating the operation of burst mode is shown in FIG. 3. Morespecifically, FIG. 3 depicts two burst mode read cycles, with each readcycle being directed to a different row of the DRAM.

To initiate a burst mode read cycle, a row address 308(1) is placed ontothe address lines 116, and a RAS signal 302(1) is asserted on the RAScontrol line 118. Then, a column address 310(1) is sent onto the addresslines 116, and a CAS signal 304(1) is asserted on the CAS control line118. In response to the column address 310(1) and the CAS signal 304(1),the DRAM internally generates a plurality of additional columnaddresses. These additional column addresses are generated based uponthe column address 310(1) that is provided, and a predetermined scheme.For example, the additional column addresses may be generated byincrementing the provided column address 310(1), decrementing the columnaddress 310(1), or by manipulating the column address 310(1) in someother manner. The number of additional column addresses generated by theDRAM depends upon the burst length that the DRAM is implementing. In theexample shown in FIG. 3, the burst length is four; thus, threeadditional column addresses are generated by the DRAM.

As the provided column address 310(1) is received, and as eachadditional column address is generated, they are applied by the DRAM toaccess a particular set of data. These addresses are applied insuccession so that multiple sets of data are accessed from the same rowof the DRAM. A short time after the application of each column address,data 306 stored at the locations indicated by the row address 308(1) andthe applied column address starts to appear on the data bus 110. Becausethis data 306 is extracted from the DRAM 100 in response to consecutiveapplications of column addresses, there is no idle time between the setsof data 306(1)-306(4) on the data bus 110. As a result, data busutilization is improved.

After the first set of data 306(1)-306(4) disappears from the data bus110, a second burst mode read operation may be initiated. Like the firstread operation, the second read operation begins with a row address308(2) on the address lines 116, and a RAS signal 302(2) on the RAScontrol line 118. Then, a column address 310(2) is sent onto the addresslines 116, and a CAS signal 304(2) is asserted on the CAS control line118. In response, the DRAM generates three additional column addresses,and applies the provided column address 310(2) and the additional columnaddresses in succession to access multiples set of data from the samerow. Shortly after each column address is applied, data 306 stored atthe locations indicated by the row address 308(2) and the applied columnaddress appears on the data bus 110. Because this data 306 is extractedfrom the DRAM 100 in response to consecutive applications of columnaddresses, there is again no idle time between the sets of data306(5)-306(8) on the data bus 110. The second read operation is thuscompleted. Additional successive reads may be carried out in a similarfashion.

Several aspects of burst mode operation should be noted. First, noticethat burst mode significantly increases output data granularity. Morespecifically, because a burst mode memory request involves multiplecolumn accesses, the data extracted from the DRAM in response to a burstmode request is not just one base granularity in size, but rather is amultiple of the base granularity, where the multiple is equal to theburst length. Thus, in the example shown in FIG. 3, the output datagranularity of the DRAM is four times the base granularity. This maypose a problem in some implementations. For example, in someapplications, a CPU may wish to access only one base granularity of dataat a time. If burst mode is implemented in such an application, then allof the data after the first granularity will be dropped by the CPU. Insuch a case, even though data bus utilization is improved by the use ofburst mode, overall system efficiency is not improved because the extradata from the memory is not used. From an efficiency point of view, theend result is the same as if burst mode were not implemented at all. Insuch applications, burst mode does not provide a useful solution.

A second aspect to note is that burst mode eliminates data bus idle timeonly so long as the same row is being accessed. As soon as a differentrow is accessed, a significant amount of idle time is introduced on thedata bus 110, as shown in FIG. 3. Thus, in applications where access ofthe DRAM switches from row to row on a regular basis (as is often thecase), there is a substantial amount of idle time on the data bus 110,even if burst mode is implemented.

To further improve data bus utilization, burst mode may be implementedin conjunction with a multi-bank DRAM to achieve full data busutilization. In a multi-bank DRAM, the DRAM is divided into multiple“banks”, which may be viewed as “virtual memories” within the DRAM. Eachbank may be accessed individually, and each bank has its own set ofsense amps. However, all banks share the same data bus. A block diagramof a sample multi-bank DRAM 400 is shown in FIG. 4. While FIG. 4 shows aDRAM 400 having four banks 404, it should be noted that more or fewerbanks may be implemented if so desired. The basic concept behind amulti-bank DRAM 400 is that higher bus utilization may be achieved by“interleaving” or alternating memory requests between the differentbanks 404. By interleaving the memory requests, it is possible toinitiate memory access to one bank (e.g. 404(1)) while another bank(e.g. 404(2)) is busy delivering data onto the data bus. By doing so,the data bus idle time of one bank is used advantageously by the otherbank to put data onto the data bus 410. Because all banks 404 are usingthe same data bus 410, interleaving the memory requests in this waymakes it possible to keep the data bus 410 constantly filled, even whendifferent rows are being accessed.

To illustrate how burst mode and interleaving may be used to achievefull data bus utilization, reference will now be made to the timingdiagram of FIG. 5. In FIG. 5, a RAS1 signal is used to indicate a RASsignal applied to bank 1 404(1), while a RAS2 signal is used to indicatea RAS signal applied to bank 2 404(2), and so on. Likewise, a CAS1signal indicates a CAS signal being applied to bank 1 404(1), while aCAS2 signal indicates a CAS signal being applied to bank 2 404(2), andso on.

As shown in FIG. 5, a read operation from bank 1 404(1) of the DRAM 400is initiated by first sending an asserted RAS signal 502(1) and a rowaddress 508(1) to bank 1 404(1). Then, at a later time, an asserted CASsignal 504(1) and a column address 510(1) are sent to bank 1 404(1). Ashort time thereafter, data associated with the row address 508(1) andthe column address 510(1) are sent onto the data bus 410 (FIG. 4) by thesense amps 408(1) of bank 1 404(1). In the timing diagram shown in FIG.5, it is assumed that bank 1 404(1) implements a burst mode length oftwo. Thus, in response to the one column address 510(1), two sets ofdata 506(1), 506(2) are outputted onto the data bus 410 by bank 1404(1).

After the RAS signal 502(1) is sent to bank 1 404(1) but before the CASsignal 504(1) is sent to bank 1 404(1), an asserted RAS signal 502(2)and a row address 508(2) are sent to bank 2 404(2) of the DRAM 400. Inaddition, an asserted CAS signal 504(2) and a column address 510(2) aresent to bank 2 404(2) at a later time. In response to these signals,bank 2 404(2) outputs data associated with the row address 508(2) andthe column address 510(2) onto the data bus 410 using the sense amps408(2). As was the case with bank 1 404(1), bank 2 404(2) alsoimplements a burst mode length of two. As a result, two sets of data506(3), 506(4) are outputted onto the data bus 410 by bank 2 404(2) inresponse to the one column address 510(2). These sets of data 506(3),506(4) immediately follow the sets of data 506(1), 506(2) outputted bybank 1; thus, there is no idle time between the data sets.

After the RAS signal 502(2) is sent to bank 2 404(2) but before the CASsignal 504(2) is sent to bank 2 404(2), an asserted RAS signal 502(3)and a row address 508(3) are sent to bank 3 404(3). A short timethereafter, an asserted CAS signal 504(3) and a column address 510(3)are sent to bank 3 404(3). In response, bank 3 404(3) outputs dataassociated with row address 508(3) and column address 510(3) onto thedata bus 410 using the sense amps 408(3). As was the case with bank 1and bank 2 404(2), bank 3 404(3) also implements a burst mode length oftwo. As a result, two sets of data 506(5), 506(6) are outputted onto thedata bus 410 by bank 3 404(3) in response to the one column address510(3). These sets of data 506(5), 506(6) immediately follow the sets ofdata 506(3), 506(4) outputted by bank 2; thus, there is no idle timebetween the data sets.

To finish the example, after the RAS signal 502(3) is sent to bank 3404(3) but before the CAS signal 504(3) is sent to bank 3 404(3), anasserted RAS signal 502(4) and a row address 508(4) are sent to bank 4404(4). A short time later, an asserted CAS signal 504(4) and a columnaddress 510(4) are sent to bank 4 404(4). In response, bank 4 404(4)outputs data associated with row address 508(4) and column address510(4) onto the data bus 410 using the sense amps 408(4). As was thecase with the other banks, bank 4 404(4) implements a burst mode lengthof two. As a result, two sets of data 506(7), 506(8) are outputted ontothe data bus 410 by bank 4 404(4) in response to the one column address510(4). These sets of data 506(7), 506(8) immediately follow the sets ofdata 506(5), 506(6) outputted by bank 3; thus, there is no idle timebetween the data sets.

While bank 4 404(4) is being accessed, access of bank 1 404(1) may againbe initiated with a RAS signal and a row address, as shown, to extractmore data from that bank. This process of interleaving accesses betweenthe various banks 404 may continue indefinitely to continually accessdata from the DRAM 400. By combining burst mode operation with amulti-bank DRAM 400 as shown in this example, it is possible to achievefull data bus utilization.

In practice, a certain number of banks are needed to achieve full databus utilization in a particular DRAM, where the number of banks neededis determined by certain timing parameters of the DRAM. One relevanttiming parameter is the minimum time required between consecutive RASsignals to the same bank. This parameter, denoted herein as Trc, isoften referred to as the RAS cycle time. Another relevant parameter isthe amount of time it takes to place one base granularity of data ontothe data bus. This parameter is denoted herein as Dt. To determine thenumber of banks needed to achieve full data bus utilization, Trc isdivided by n*Dt where n is the burst length. If, for example, Trc is 80ns and Dt is 10 ns and the DRAM is implementing a burst length of two,then the number of banks needed is 80 ns/20 ns or four. With thesetiming parameters (which are typical) and four banks, a DRAM can achievefull data bus utilization.

While the combination of burst mode and a multi-bank DRAM 400 makes itpossible to achieve 100% data bus utilization in a memory, thisimplementation does not come without its drawbacks. One significantdrawback is that it still relies upon burst mode to achieve full databus utilization. Because of this reliance, this implementation suffersfrom the same shortcoming as that experienced in regular burst mode.Namely, it increases the data granularity of the DRAM 400. Notice fromthe timing diagram of FIG. 5 that instead of outputting just one basegranularity of data per access to each bank, the DRAM 400 outputs two(it is two in the example shown in FIG. 5 but it could more than two inother implementations). This increase in data granularity can lead toinefficiency.

As noted previously, in some applications, an external component (suchas a CPU) may wish to access only one base granularity of data at atime. In such applications, any data provided after the first basegranularity will be dropped. If burst mode is implemented in such anapplication, at least half of the data provided by the DRAM 400 will bedropped, which means that at most 50% efficiency can be achieved. Thus,even though burst mode combined with a multi-bank DRAM 400 may achieve100% data bus utilization in such an application, it does not improveoverall system efficiency because the extra data is not used.Consequently, the burst mode/multi-bank DRAM combination does notprovide a complete solution for all possible applications.

As an alternative to the burst mode/multi-bank DRAM combination, aplurality of separate DRAM's may be implemented to achieve full data busutilization. By interleaving memory requests between separate DRAM'sinstead of between separate banks within a single DRAM, it is possibleto achieve full data bus utilization without requiring an increase indata granularity. This result comes with extra cost and complexity,however. To illustrate how separate DRAM's may be used to achieve fulldata bus utilization, reference will be made to FIGS. 6 and 7.Specifically, FIG. 6 shows a block diagram of a sample multi-DRAMimplementation, while FIG. 7 shows a timing diagram for several readcycles of the implementation of FIG. 6.

As shown in FIG. 6, the sample implementation comprises a plurality ofseparate DRAM's 604(1), 604(2) (more than two may be implemented if sodesired), with each DRAM 604 having its own separate command lines608(1), 608(2), and address lines 606(1), 606(2). Both DRAM's share thesame data bus 620, and both have 2 banks. In addition to the DRAM's604(1), 604(2), the implementation further comprises a controller 602for controlling the interleaving of requests between the DRAM's 604(1),604(2). It is the responsibility of this controller 602 to manage theinterleaving of memory requests such that: (1) the data bus 620 is usedas fully as possible; and (2) there is no bus contention on the data bus620.

To illustrate how the implementation of FIG. 6 can be used to achievefull data bus utilization, reference will be made to the timing diagramof FIG. 7. For clarity purposes, RAS1,1 is used in FIG. 7 to indicate aRAS command applied to DRAM 1 604(1), bank 1, while RAS2,1 is used toindicate a RAS command applied to DRAM 2 604(2), bank 1, and so on.Likewise, CAS1,1 is used to indicate a CAS command being applied to DRAM1 604(1), bank 1, while CAS2,1 is used to indicate a CAS command beingapplied to DRAM 2 604(2), bank 1.

As shown in FIG. 7, to extract data from the DRAM's 604(1), 604(2), thecontroller 602 first initiates a read operation on DRAM 1 604(1), bank1. This is carried out by sending a RAS command 702(1) and a row address706(1) to DRAM 1 604(1), bank 1. Then, a CAS command 704(1) and a columnaddress 706(2) are sent to DRAM 1 604(1), bank 1. A short timethereafter, data 720(1) associated with the row address 706(1) and thecolumn address 706(2) are outputted onto the data bus 620 (FIG. 6) byDRAM 1 604(1), bank 1. While the CAS command 704(1) and the columnaddress 706(2) are being sent to DRAM 1 604(1), bank 1, the controller602 also sends a RAS command 712(1) and a row address 716(1) to DRAM 2604(2), bank 1. Thereafter, a CAS command 714(1) and a column address716(2) are sent to DRAM 2 604(2), bank 1. In response to these signals,DRAM 2 604(2), bank 1, outputs data 720(2) associated with the rowaddress 716(1) and the column address 716(2) onto the data bus 620. Thisset of data 720(2) immediately follows the set of data 720(1) outputtedby DRAM 1 604(1), bank 1; thus, there is no idle time between the datasets.

While the CAS signal 714(1) and the column address 716(2) are being sentto DRAM 2 604(2), bank 1, a RAS command 702(2) and row address 706(3)are sent to DRAM 1 604(1), bank 2, to initiate another read cycle.Thereafter, a CAS command 704(2) and a column address 706(4) are sent toDRAM 1 604(1), bank 2. In response, DRAM 1 604(1), bank 2, outputs data720(3) associated with the row address 706(3) and the column address706(4) onto the data bus 620. This set of data 720(3) immediatelyfollows the set of data 720(2) outputted by DRAM 2 604(2), bank 1; thus,there is again no idle time between the data sets. To finish theexample, while the CAS command 704(2) and the column address 706(4) arebeing sent to DRAM 1 604(1), bank 2, the controller 602 initiates a readcycle on DRAM 2 604(2), bank 2, by sending a RAS command 712(2) and arow address 716(2) to DRAM 2 604(2), bank 2. Thereafter, a CAS command714(2) and a column address 716(4) are sent to DRAM 2 604(2), bank 2. Inresponse to these signals, DRAM 2 604(2), bank 2, outputs data 720(4)associated with the row address 716(3) and the column address 716(4)onto the data bus 620. This set of data 720(4) immediately follows theset of data 720(3) outputted by DRAM 1 604(1), bank 2; hence, there isno idle time between the data sets. Additional read operations may becarried out in this manner to continue extracting data from the DRAM's604(1), 604(2). As this example illustrates, by interleaving memoryrequests between multiple banks of multiple DRAM's, it is possible toachieve full data bus utilization, and because no burst mode isimplemented, data granularity is not increased.

While the multi-DRAM implementation is able to achieve full data busutilization without increasing data granularity, it does so at asignificant cost. First, due to the tight timing constraints, the DRAM'sshown in FIG. 6 are very fast and very expensive. With multiple DRAM'sbeing required to implement the system of FIG. 6, the cost of the memorysystem can be prohibitive. Compared to single DRAM memory systems, thecost of this multi-DRAM system can be several-fold. Also, the multi-DRAMimplementation is limited in its application. By its very nature, it canbe implemented only in a multi-DRAM environment. In the manyapplications in which it is desirable to implement just one DRAM, themulti-DRAM implementation cannot be used. In addition, thisimplementation can add substantial complexity to the memory accessprocess. Because the controller 602 must concurrently control multipleDRAM's, the memory access process is much more complex and difficult tomanage than in a single DRAM implementation. Overall, there is asignificant price to pay for the functionality provided by themulti-DRAM configuration, and in many implementations, this price isprohibitive. Hence, the multiple DRAM approach does not provide a viablesolution for all applications.

SUMMARY

In view of the shortcomings of the prior art, the present inventionprovides an improved mechanism, which enables full data bus utilizationto be achieved within a memory, but which does not increase the datagranularity of the memory or require multiple memories to beimplemented. In accordance with one embodiment, there is provided amemory comprising a first memory portion, a second memory portion, andan interface. To enable the memory portions to be manipulatedindependently, the memory portions in one embodiment are electricallyisolated from each other. In one embodiment, this electrical isolationis achieved by physically placing the interface between the memoryportions. In addition, the interface is adapted, in one embodiment, toenable it to receive a row command and a column command in the time ittakes to cycle the memory once (to read one base granularity of data outof or write one base granularity of data into the memory). With such amemory, it is possible to achieve full data bus utilization withoutincreasing data granularity.

In one embodiment, full data bus utilization is achieved by interleavingaccess requests between the two memory portions. More specifically, theinterface receives a first access request (comprising a row command andno more than one column command) on a set of control ports, and forwardsthe request on to the first memory portion for processing. In response,the first memory portion accesses a first set of data having a size ofno more than one base granularity, and sends that data onto a data bus(assuming a read operation). A data set is thus extracted from thememory. Thereafter, the interface receives a second access request onthe same set of control ports, and forwards the request to the secondmemory portion for processing. In response, the second memory portionaccesses a second set of data also having a size of no more than onebase granularity, and sends that data onto the data bus. If the accessrequests are timed properly relative to each other, then the second setof data will be sent onto the data bus immediately after the first setof data such that there is substantially no idle time on the data bus.With no data bus idle time, full data bus utilization is achieved. Thisfull data bus utilization may be perpetually maintained by continuouslyinterleaving access requests between the two portions. In oneembodiment, proper relative timing between the various access requestsis made possible, as least partially, by the fact that the memoryportions are electrically isolated from each other, and hence, may beindependently manipulated, and by the fact that a row command and acolumn command can be received by the interface in the time it takes tocycle either memory portion once.

Notice that full data bus utilization is achieved without increasingdata granularity. More specifically, notice that burst mode does notneed to be implemented, and that no more than one base granularity ofdata is sent onto the data bus in response to each access request. Inaddition, notice that full data bus utilization is achieved withoutimplementing multiple memories. The different memory portions may behavelike independent memories, but they are both part of the same memoryusing the same set of control ports. Thus, multiple memories need not beimplemented. By achieving full data bus utilization without increasingdata granularity and without implementing multiple memories, the presentinvention provides a significant advance over the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of a typical DRAM.

FIG. 2 is a timing diagram illustrating the steps carried out by theDRAM of FIG. 1 during several read cycles.

FIG. 3 is a timing diagram illustrating the steps carried out duringseveral burst mode read cycles.

FIG. 4 is a block diagram of a sample multi-bank DRAM.

FIG. 5 is a timing diagram illustrating the operation of the DRAM ofFIG. 4 during several read cycles.

FIG. 6 is a block diagram of a multiple DRAM implementation.

FIG. 7 is a timing diagram illustrating the operation of theimplementation shown in FIG. 6 during several read cycles.

FIG. 8 is a block diagram of a system in which one embodiment of thepresent invention may be implemented.

FIG. 9 is a detailed block diagram of a memory in accordance with oneembodiment of the present invention.

FIG. 10 is a timing diagram illustrating the operation of the memoryshown in FIG. 9 during several read cycles.

FIG. 11 is a timing diagram illustrating an alternative operation of thememory of FIG. 9 wherein a single set of control ports/lines is used tosend both row and column commands.

FIG. 12 is a flow diagram illustrating the operation of the memorycontroller of FIG. 8 in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENT(S)

With reference to FIG. 8, there is shown a block diagram of a system 800in which one embodiment of the present invention may be implemented, thesystem 800 comprising a memory 802, a memory controller 804, and anexternal component 806. For purposes of illustration, it will be assumedin the following discussion that memory 802 is a dynamic random accessmemory (DRAM). However, it should be noted that the teachings of thepresent invention may be applied to other types of memory as well, if sodesired. In one embodiment, memory 802 is implemented as an integratedcircuit.

In system 800, the external component 806 (which may, for example, be aCPU executing a program) is the component that requires access to thememory 802 for purposes of writing data into the memory 802, readingdata out of the memory 802, or both. To access the memory 802, theexternal component 806 submits requests to the memory controller 804 viaa set of control 830 and data lines 832. In response, the memorycontroller 804 translates the requests into access requests that thememory 802 can understand, and sends the access requests to the memory802 via another set of control 822 and data lines 820. In the case of awrite, data is provided to the memory 802 via the data lines 820. In thecase of a read, data is provided by the memory 802 to the controller 804via the data lines 820.

The interface 810 of the memory 802 receives the access requests fromthe controller 804 and responds by accessing the memory portions 812(1),812(2) of the memory 802. In one embodiment, the interface 810 accesseswhichever portion 812(1), 812(2) is indicated in an access request.Since it is the controller 804 that generates the access requests, it isthe controller 804 that controls which portions 812(1), 812(2) of thememory 802 are accessed and in what sequence. As will be discussed in alater section, it is desirable to interleave access requests between thedifferent portions 812(1), 812(2) to achieve full data bus utilization.Since it is the controller 804 that controls which memory portions812(1), 812(2) are accessed, it is up to the controller 804 to properlyinterleave the access requests between the portions 812(1), 812(2) toenable full data bus utilization. The operation of the controller 804will be described in greater detail in a later section. In theembodiment shown in FIG. 8, the memory 802 is depicted as comprising twoportions 812(1), 812(2). It should be noted that this is forillustrative purposes only. If so desired, the memory 802 may beimplemented with any number of portions. Each portion 812 may compriseone or more banks. In the following description, for the sake ofsimplicity, it will be assumed that each portion 812 comprises one bank.However, it should be noted that for purposes of the present invention,each portion 812 may comprise 1 to n banks, where n is any integer.

With reference to the block diagram of FIG. 9, an embodiment of thememory 802 will now be described in greater detail. As shown in FIG. 9,the memory 802 comprises an interface 810, and two memory portions812(1), 812(2). The first memory portion 812(1) comprises a bank with aplurality of memory/storage cells 902(1) arranged in rows and columns,and a row decoder 904(1) and column decoder 906(1) for facilitatingaccess to the memory cells 902(1). In addition, the first memory portion812(1) comprises a set of sense amps 908(1) coupled to a data bus 820for receiving data therefrom and sending data thereto. Similarly, thesecond memory portion 812(2) comprises a bank with a plurality ofmemory/storage cells 902(2) arranged in rows and columns, and a rowdecoder 904(2) and column decoder 906(2) for facilitating access to thememory cells 902(2). In addition, the second memory portion 812(2)comprises a set of sense amps 908(2) coupled to the data bus 820 forreceiving data therefrom and sending data thereto.

In one embodiment, the memory portions 812(1), 812(2) may be treatedlike independent memories. That is, each portion 812 may be accessedindependently of the other portion 812 from a timing standpoint. Morespecifically, portion 812(1) may be accessed at any time relative to theaccessing of portion 812(2), and portion 812(2) may be accessed at anytime relative to the accessing of portion 812(1). Put another way, notiming constraint is imposed on when one portion may be accessedrelative to the other. Thus, there is no minimum required time delaybetween accessing one portion 812(1) and accessing the other portion812(2). This is quite different from typical DRAM's, which usuallyrequire a time delay between successive accesses to the same DRAM, evenif it is to different banks. As will be explained further below, this“independent” nature of the memory portions 812 greatly facilitates theprocess of interleaving access requests between the portions 812(1),812(2) to achieve full data bus utilization without increasing datagranularity. At this point, it should be noted that while the memoryportions 812(1), 812(2) may be treated like independent memories from anaccessing point of view, they are still part of the same memory 802.They share the same data bus 820, the same interface 810, and the samecontrol ports/lines 822. Thus, unlike the multi-DRAM implementationdiscussed previously, the memory 802 is a single memory, not multiple,separate memories.

In one embodiment, the independent nature of the memory portions 812 isderived from that fact that they are electrically isolated from eachother. By electrically isolated, it is meant that the two portions812(1), 812(2) are sufficiently decoupled from each other from anelectrical noise standpoint that the access of one portion does notcorrupt data in the other portion. More specifically, the activation ofone set of sense amps 908 does not corrupt data in the other set ofsense amps 908, regardless of the timing of the activations. As a resultof this electrical isolation, it is possible to activate the sets ofsense amps 908(1), 908(2) independently to process access requestswithout fear that processing an access request in one portion 812 willadversely affect the processing of an access request in the otherportion.

In one embodiment, the electrical isolation between the memory portions812(1), 812(2) is achieved by physically placing the interface 810between the two portions 812(1), 812(2). The interface 810 provides anatural and convenient barrier between the two portions 812(1), 812(2)and works effectively to electrically isolate one portion 812(1) fromthe other 812(2). It should be noted that this is just one possible wayof achieving electrical isolation between the portions 812(1), 812(2).The same result may be achieved in many other ways (e.g. improved senseamp circuits, better power supply control, circuit enhancements, etc.).All such means for electrically isolating the portions 812(1), 812(2)are within the scope of the present invention.

As noted above, both memory portions 812(1), 812(2) share the interface810 and the control ports/lines 822. In one embodiment, the interface810 receives all access requests via the control ports/lines 822 andforwards the requests on to the proper memory portion 812(1), 812(2) forprocessing. In effect, the interface 810 acts as a manager to manage theprocessing of access requests by the memory portions 812(1), 812(2). Incarrying out its management function, the interface 810 receives severalsets of information on the control ports/lines 822 from the controller804 for each access request. In one embodiment, these sets ofinformation include: (1) portion selection information 924 thatspecifies which memory portion 812(1), 812(2) is to be accessed; (2) rowcontrol information 920 that specifies which row of storage cells withina memory portion is to be accessed; and (3) column control information922 that specifies which column or columns of storage cells within thatrow are to be accessed. Together, these sets of information provide allof the information needed to access one base granularity of data fromone of the portions 812(1), 812(2) of the memory 802.

With regard to the row and column control information 920, 922, thesesets of information may be sent in any desired format. For example, therow control information 920 may take the form of a row command (e.g.comprising a row address and a RAS) sent as a set of parallel bits, orit may take the form of a row command sent as a serialized packet, or itmay take any other form. So long as sufficient information is providedto the interface 810 to instruct the interface 810 to access aparticular row of storage cells, any row command format may be used. Thesame is true for the column control information 922. Specifically, thecolumn control information 922 may take the form of a column command(e.g. comprising a column address and a CAS) sent as a set of parallelbits, or it may take the form of a column command sent as a serializedpacket, or it may take any other form. So long as sufficient informationis provided to the interface 810 to instruct the interface 810 to accessone or more particular columns of storage cells, any column commandformat may be used.

In response to the control information on the control ports/lines 822,the interface 810 manages the operation of the memory portions 812(1),812(2). In one embodiment, the interface 810 is capable of receivingboth a row command and a column command from the controller 804 in anamount of time X, where X is less than or equal to the amount of time Tit takes to cycle either of the memory portions 812(1), 812(2) once.Used in this context, the amount of time T it takes to cycle the memory802 is the amount of time needed to read one base granularity of dataout of, or write one base granularity of data into either portion812(1), 812(2) of the memory 802. As defined previously, the basegranularity of the memory 802 refers to the amount of data that is readout of or written into the memory 802 in response to each column command(when no burst mode is implemented). With this ability to receive both arow command and a column command in the time it takes to cycle thememory 802 once, the interface 810 greatly facilitates the process ofachieving full data bus utilization without increasing data granularity.As will be explained more fully in a later section, the row command andthe column command received by the interface 810 in the amount of time Xmay correspond to different access requests due to the process ofpipelining.

To illustrate how the memory 802 may be used advantageously to achievefull data bus utilization, reference will now be made to the timingdiagram of FIG. 10, which shows eight read access requests interleavedbetween the two portions 812(1), 812(2). For the sake of simplicity,FIG. 10 shows only read cycles. However, it should be noted that writeoperations may be carried out in a similar fashion. For purposes ofexplanation, the following nomenclature will be used in FIG. 10: (1) P1will be used to indicate an access request to the first portion 812(1)of the memory, while P2 will be used to indicate an access request tothe second portion 812(2); (2) Row1 will be used to indicate a rowcommand to portion 812(1), while Row2 will be used to indicate a rowcommand to portion 812(2); and (3) Col1 will be used to indicate acolumn command to portion 812(1), while Col2 will be used to indicate acolumn command to portion 812(2). With this in mind, the operation ofthe memory 802 will now be described.

Initially, the interface 810 receives a first access request from thecontroller 804 to read a set of data from the first portion 812(1) ofthe memory 802. This first access request comprises a portion indication1002(1) sent on the portion control port/line 924, a row command 1004(1)sent on the row control ports/lines 920, and a column command 1006(1)sent on the column control ports/lines 922. In the embodiment shown, therow command 1004(1) is sent first and the column command 1006(1) is sentlater. In a synchronous DRAM (SDRAM), the row command 1004(1) and thecolumn command 1006(1) may be sent in consecutive clock cycles. Uponreceiving this access request, the interface 810 determines that it isintended for the first memory portion 812(1); hence, it forwards the rowcommand 1004(1) and the subsequent column command 1006(1) on to portion812(1).

In response, the row decoder 904(1) of the first memory portion 812(1)decodes the row address contained in the row command 1004(1). Thiscauses one of the rows of storage cells 902(1) to be accessed, and thedata contained therein to be loaded into the sense amps 908(1). Inaddition, the column decoder 906(1) of the first portion 812(1) decodesthe column address contained in the column command 1006(1), which causesa subset of the data contained in the sense amps 908(1) to be sent ontothe data bus 820. This output data 1008(1) appears on the data bus 820 ashort time after the first access request is received, and is one basegranularity in size (because the access request contained only onecolumn command and burst mode was not implemented). A first set of data1008(1) is thus extracted from the memory 802.

While the first access request is being processed, the interface 810receives a second access request from the controller 804 to read a setof data from the second portion 812(2) of the memory 802. This secondaccess request comprises a portion indication 1002(2) sent on theportion control port/line 924, a row command 1004(2) sent on the rowcontrol ports/lines 920, and a column command 1006(2) sent on the columncontrol ports/lines 922. As was the case with the first access request,the row command 1004(2) is sent first and the column command 1006(2) issent later. Notice from the embodiment shown in FIG. 10 that the rowcommand 1004(2) of the second access request is sent concurrently withthe column command 1006(1) of the first access request. This pipeliningof the different parts of different access requests facilitates theprocess of interleaving access requests to the different memory portions812. In one embodiment, both the row command 1004(2) and the columncommand 1006(1) are received in an amount of time X, which is less thanor equal to the time T needed to cycle either of the memory portions812(1), 812(2) once. The ability of the controller 804 to send, and theability of the interface 810 to receive, both a row command and a columncommand in an amount of time X less than or equal to T contributes tothe system's ability to achieve full data bus utilization withoutincreasing data granularity.

Another point to note in the example shown in FIG. 10 is that the rowcommand 1004(2) of the second access request is received immediatelyafter the row command 1004(1) of the first access request. There is norequired minimum time delay between the two commands 1004(1), 1004(2).In an SDRAM, the row commands 1004(1), 1004(2) may be received inconsecutive clock cycles. In one embodiment, this is made possible bythe fact that the two memory portions 812(1), 812(2) are electricallyisolated from each other, and hence, may be treated like independentmemories. Because the two memory portions 812(1), 812(2) may be treatedlike independent memories, it is possible to receive and forward anaccess request to one of the memory portions 812(1), 812(1) withoutregard to the other. This in turn means that there is no timingrestriction on when a row command may be sent to one memory portionrelative to a row command being sent to the other memory portion. Aswill be discussed further below, this lack of a timing constraintbetween the row commands facilitates the process of achieving full databus utilization without increasing data granularity.

Upon receiving the second access request, the interface 810 determinesthat it is intended for the second memory portion 812(2); hence, itforwards the request on to portion 812(2). In response, the row decoder904(2) of the second memory portion 812(2) decodes the row addresscontained in the row command 1004(2). This causes one of the rows ofstorage cells 902(2) to be accessed, and the data contained therein tobe loaded into the sense amps 908(2). In addition, the column decoder906(2) of the second portion 812(2) decodes the column address containedin the column command 1006(2), which causes a subset of the datacontained in the sense amps 908(2) to be sent onto the data bus 820.This output data 1008(2) appears on the data bus 820 a short time afterthe second access request is received, and like the first set of data1008(1), is one base granularity in size. If the second access requestis properly timed relative to the first access request, then the secondset of data 1008(2) will be sent onto the data bus 820 immediately afterthe first set of data 1008(1) so that there is substantially no idletime between the data sets 1008(1), 1008(2). With no data bus idle timebetween the data sets 1008(1), 1008(2), full data bus utilization isachieved.

While the second access request is being processed, the interface 810receives a third access request, this one being directed back to thefirst memory portion 812(1). Like the first two access requests, thethird access request comprises a portion indication 1002(3), a rowcommand 1004(3), and a column command 1006(3). The row command 1004(3)is received first and the column command 1006(3) is received later. Asshown, the row command 1004(3) is received immediately after the rowcommand 1004(2) of the second access request and is receivedconcurrently with the column command 1006(2) of the second accessrequest. The row command 1006(3) and the column command 1006(2) arereceived in an amount of time X, which is less than or equal to theamount of time T needed to cycle either of the memory portions 812(1),812(2) once.

Upon receiving this third access request, the interface 810 determinesthat it is intended for the first memory portion 812(1); hence, itforwards the request on to portion 812(1). In response, the row decoder904(1) and the column decoder 906(1) of the first portion 812(1) decodethe row address and the column address contained in the row command1006(3) and column command 1006(3), respectively, and cause a basegranularity of data to be sent from the sense amps 908(1) onto the databus 820 (in the manner already described). This output data 1008(3)appears on the data bus 820 a short time after the third access requestis received, and like the first two sets of data 1008(1), 1008(2), isone base granularity in size. If the third access request is properlytimed relative to the second access request, then the third set of data1008(3) will be sent onto the data bus 820 immediately after the secondset of data 1008(2). Thus, there is substantially no idle time betweenthe data sets 1008(2), 1008(3), which in turn enables full data busutilization to be achieved.

While the third access request is being processed, the interface 810receives a fourth access request, this one being directed back to thesecond memory portion 812(2). Like the previous requests, the fourthaccess request comprises a portion indication 1002(4), a row command1004(4), and a column command 1006(4). The row command 1004(4) isreceived first and the column command 1006(4) is received later. Asshown, the row command 1004(4) is received immediately after the rowcommand 1004(3) of the third access request and is received concurrentlywith the column command 1006(3) of the third access request. The rowcommand 1006(4) and the column command 1006(3) are received in an amountof time X, which is less than or equal to the amount of time T needed tocycle either of the memory portions 812(1), 812(2) once.

Upon receiving this fourth access request, the interface 810 determinesthat it is intended for the second memory portion 812(2); hence, itforwards the request on to portion 812(2). In response, the row decoder904(2) and the column decoder 906(2) of the second portion 812(2) decodethe row address and the column address contained in the row command1006(4) and column command 1006(4), respectively, and cause a basegranularity of data to be sent from the sense amps 908(2) onto the databus 820 (in the manner already described). This output data 1008(4)appears on the data bus 820 a short time after the third access requestis received, and like the previous sets of data 1008(1), 1008(2),1008(3), is one base granularity in size. If the fourth access requestis properly timed relative to the third access request, then the fourthset of data 1008(4) will be sent onto the data bus 820 immediately afterthe third set of data 1008(3). Thus, there is substantially no idle timebetween the data sets 1008(3), 1008(4), which in turn enables full databus utilization to be achieved. In the manner described, access requestsmay be continuously interleaved between the portions 812(1), 812(2) ofthe memory 802 to achieve sustained full data bus utilization, and sinceneither burst mode nor a multiple memory configuration is implemented,this full data bus utilization is achieved without increasing datagranularity and without implementing multiple memories. Thus, full databus utilization is achieved without the shortcomings of the prior art.

To facilitate a complete understanding of the invention, a comparisonwill now be made between the timing diagram of FIG. 10 and the timingdiagram of FIG. 5, which shows the operation of the prior art multi-bankDRAM of FIG. 4. Several points should be noted with regard to the timingdiagram of FIG. 5. First, note that in FIG. 5, the DRAM 402 requiresmore time to receive a complete access request than it does to place onegranularity of data 506 onto the data bus 410. More specifically, toreceive a complete access request, the DRAM 402 has to: (1) receive aRAS signal and a row address; and then (2) receive a CAS signal and acolumn address. In that same amount of time, two base granularities ofdata can be accessed and placed onto the data bus 410 (i.e. the DRAM 402can be cycled twice), as shown. Because the DRAM 402 takes longer toreceive a complete request than it does to cycle the memory once, theDRAM 402 cannot keep the data bus 410 full unless it accesses severalbase granularities of data in response to each access request (i.e.implements burst mode). Unfortunately, by implementing burst mode, theDRAM 402 increases its output data granularity. As discussed previously,this has undesirable consequences.

The memory 802 of FIG. 9 has no such problem. Because the controller 804is able to send, and the interface 810 of memory 802 is able to receive,both a row command and a column command (even though they may correspondto different access requests) in the time it takes to cycle the memory802 once, memory 802 is not required to implement burst mode. Hence,memory 802 is able to achieve full data bus utilization withoutincreasing data granularity, as shown in FIG. 10.

Another point to note with regard to FIG. 5 is that DRAM 402 has a timeconstraint, commonly referred to as Trr, which precludes it fromreceiving one RAS signal (i.e. a row command) immediately after another.More particularly, the DRAM 402 is required to wait at least a Trrperiod of time between successive RAS signals, even if the RAS signalsare directed to different banks. This time constraint is due, at leastin part, to the fact that the banks 404(1), 404(2) of DRAM 402 are notelectrically isolated from each other.

To elaborate, when a row of memory cells is accessed in response to arow command, one of the sets of sense amps 408 is activated. Theactivation of one of the sets of sense amps 408 causes a current spike,which in turn causes electrical noise. In a typical multi-bank DRAM 402,there is no electrical isolation between the various banks 404; hence,the noise generated in one set of sense amps 408 is felt in the other.To prevent the noise from one set of sense amps 408 from corrupting thedata in the other set of sense amps 408, it is typically necessary towait a Trr period of time between successive sense amp activations.Because of this time constraint, there is a minimum required time delayof Trr between successive row commands. This is so even if the rowcommands are directed to different banks 404 of the DRAM 402. As aresult of this time constraint, the time period between successive rowcommands is lengthened. With this lengthened time period, it is verydifficult if not impossible for the DRAM 402 to receive a completeaccess request in the time it takes to cycle the DRAM 402 once. As aresult, DRAM 402 is unable to achieve full data bus utilization withoutimplementing burst mode.

Again, the memory 902 of FIG. 9 has no such problem. Because the memoryportions 812(1), 812(2) are electrically isolated from each other, noisefrom one portion 812 does not affect the other. As a result, there is norequired minimum time delay between successive sense amp activations inthe different portions 812, which in turn means that there is norequired minimum time delay between successive interleaved row commands.As shown in FIG. 10, interleaved row commands 1004 may be received andpassed on to the different memory portions 812 in immediate succession,if so desired. By eliminating the Trr time constraint, memory 802 makesit possible to time the access requests such that data sets 1008 areplaced onto the data bus 820 in immediate succession with substantiallyno intervening idle time. By eliminating data bus idle time, full databus utilization is achieved. As noted previously, this is accomplishedwithout increasing data granularity and without implementing multipleseparate memories. Hence, memory 802 represents a significantimprovement over the prior art.

Thus far, the operation of the system 800 has been described only withreference to read operations. It should be noted, though, that the sameconcepts, timing, sequence of commands, and data ordering may be appliedto write operations. The main difference is that instead of the memory802 sending data onto the data bus 820 to the controller 804, thecontroller 804 is sending data onto the data bus 820 to the memory 802.More specifically, in a read operation, the memory 802: (1) accesses arow of data from one of the memory portions 812; (2) loads that datainto one of the sets of sense amps 908; and (3) outputs a portion of thedata in the sense amps 908 onto the data bus 820. In a write operation,the memory 802: (1) accesses a row of data from one of the memoryportions 812; (2) loads that data into one of the sets of sense amps908; (3) obtains a set of write data from the data bus 820; (4) loadsthe write data into a portion of one of the sets of sense amps 908; and(4) stores the data in the sense amps 908 back into the appropriate row.As this discussion shows, the difference between a read and a writeoperation resides mainly in the direction of the flow of data. Withregard to the timing of the portion control signals, the row and columncommands, and even the data sets on the data bus, all may remain thesame as that shown in FIG. 10 for read operations. In a write operation,it will be up to the controller 804 to send the data onto the data bus820 at the proper time.

Thus far, memory 802 has been described as having separate row control920 and column control 922 ports/lines, and as receiving row and columncommands concurrently on those ports/lines. While this is one possibleembodiment, it should be noted that other embodiments are also possible.For example, if so desired, one set of control lines may be multiplexedto carry both the row command and the column command, as shown in thetiming diagram of FIG. 11. This may be carried out, for example, byrunning the single set of control lines at double speed, or by sending arow command and a column command on different halves of a clock cycle.So long as a row command and a column command can be received in thetime it takes to cycle the memory 802 once, any method/configuration forsupplying the row command and column command may be used/implemented.

As note previously, in one embodiment, it is the memory controller 804(FIG. 8) that controls the accessing of data from the memory 802. Inparticular, it is the controller 804 that controls the sending of accessrequests to the memory 802, and the interleaving of access requests tothe different portions 812 of the memory 802 (as shown in FIG. 10). Incarrying out this function, the controller 804 has the ability to send arow command and a column command to the memory 802 in an amount of timeX, where X is less than or equal to the amount of time T that it takesto cycle the memory once, and has the logic for properly controlling thetiming of the access requests.

In controlling the timing of the access requests, the controller 804 inone embodiment implements the following rule. If two consecutive accessrequests are directed to different portions 812 of the memory 802, thenthe access requests may be timed such that they cause the data bus 820to be fully utilized (i.e. no data bus idle time between successive datasets, as shown in FIG. 10). Because the access requests are directed todifferent portions 812 of the memory 802, there is no required minimumtime delay between the access requests (i.e. between the row commands ofthe access requests).

On the other hand, if two consecutive requests are directed to the samememory portion 812, then the controller 804 imposes a delay between therow commands of the access requests, if necessary. This delay may, forexample, be equal to Trr. Because the access requests will cause thesame set of sense amps to be activated, this delay is implemented toprevent data errors. The operation of the controller 804 is shown in theflow diagram of FIG. 12.

In operation, the controller 804 receives (1202) a request from theexternal component 806 to access the memory 802. In response, thecontroller 804 translates (1204) the request to derive an access requestthat the memory 802 can understand. In one embodiment, based upon therequest, the controller 804 generates a set of portion controlinformation, a row command, and a column command. Based upon the accessrequest, the controller 804 determines (1206) the memory portion 812that needs to be accessed to service this request. If this portion 812is determined (1208) by the controller to be the same portion as thataccessed by the access request immediately preceding the current accessrequest, then the controller 804 imposes (1210) a time delay, ifnecessary. More specifically, the controller 804 determines whether acertain amount of time, such as Trr, has passed since the row command ofthe previous access request was sent to the memory 802. If not, then adelay is imposed to ensure that the proper amount of time has passedbefore sending the row command of the current access request to thememory 802. Once the proper amount of time has passed, the controller804 sends (1212) the current access request (comprising a row commandand a subsequent column command) to the memory 802. The controller 804loops back to receive (1202) another request from the external component806.

Returning to (1208), if the controller 804 determines that the currentaccess request is not directed to the same memory portion 812 as theimmediately preceding access request, then it proceeds to determine(1214) the proper timing for sending the current access request relativeto the previous access request. In doing so, the controller 804 (whenpossible) times the sending of the current access request such that itcauses the memory 802 to output data onto the data bus 820 (in the caseof a read operation) with substantially no idle time between data sets.By doing so, the controller 804 enables the memory 802 to achieve fulldata bus utilization. In some cases, it may not be possible for thecontroller 804 to time the requests such that full data bus utilizationis achieved. For example, when there is a large time interval betweenrequests from the external component 806, it may not be possible for thecontroller 804 to send access requests which are close enough in time toachieve full data bus utilization. In such cases, the controller 804sends the current access request immediately to the memory 802 tominimize idle time on the data bus.

A point to note is that since the current access request is directed toa different memory portion than the immediately preceding accessrequest, the controller 804 does not need to impose any minimum timedelay between the sending of the access requests. Thus, if so desired,the row command of the current access request may be sent immediatelyafter the row command of the preceding access request. In an SDRAM, therow command of the preceding access request and the row command of thecurrent access request may be sent in consecutive clock cycles. Once theproper timing is determined, the controller 804 sends (1212) the currentaccess request to the memory 802 at the proper time to cause the memory802 to be accessed. The controller 804 loops back to receive (1202)another request from the external component 806. In the mannerdescribed, the controller 804 interleaves access requests between thememory portions 812 whenever possible to enable full data busutilization. At the same time, it imposes time delays when necessary toprevent data errors.

At this point, it should be noted that although the invention has beendescribed with reference to a specific embodiment, it should not beconstrued to be so limited. Various modifications may be made by thoseof ordinary skill in the art with the benefit of this disclosure withoutdeparting from the spirit of the invention. Thus, the invention shouldnot be limited by the specific embodiments used to illustrate it butonly by the scope of the appended claims.

1. (canceled)
 2. A memory device, comprising: at least two electricallyisolated memory portions, each portion including banks of memory andcircuitry to write and read data to the respective bank in associationwith memory write and read transactions; interface circuitry to receivecommands and to exchange the write and read data external to theapparatus in association with the memory write and read transactions;and logic to identify based on the commands one of the at least twoelectrically isolated portions that is the target of each transaction ofthe memory write and read transactions, and to route said each write andread transaction to said target.
 3. The memory device of claim 2,wherein: the memory device is to receive serialized packets comprisingcommand information for each transaction; and the command informationcomprises a portion indication and memory address information.
 4. Thememory device of claim 2, wherein: each transaction of the memory writeand read transactions is commanded using address information comprisinga portion indication, row address information and column addressinformation; and the address information is received via at least oneexternal link in a manner not separated by idle time consisting of oneor more clock cycles.
 5. The memory device of claim 4, wherein each ofthe banks comprise dynamic random access memory (DRAM) cells.
 6. Thememory device of claim 2, wherein the memory device is characterized ashaving no timing constraint imposed on when a first portion of the atleast two electrically isolated portions can be accessed relative to asecond portion of the at least two electrically isolated portions. 7.The memory device of claim 6, wherein each given portion of the at leasttwo electrically isolated portion is characterized by a timingconstraint, Trr, that must elapse between row activations within thegiven portion.
 8. The memory device of claim 2, wherein each givenportion of the at least two electrically isolated portions is isolatedin a manner that sense amplifier activation for a bank in the givenportion does not corrupt concurrent data access in another portion ofthe at least two electrically isolated portions.
 9. The memory device ofclaim 2, wherein the memory device is to receive the commands via pluralcommunication links external to the memory device.
 10. The memory deviceof claim 2, wherein the memory device is to receive both row command andcolumn command information in multiplexed fashion over a single set ofexternal control lines.
 11. The memory device of claim 10, wherein thememory device is to receive both a row command and a column commandwithin an interval no greater than time needed to cycle column accesscircuitry once for one of the banks.
 12. The memory device of claim 2,wherein the memory device is to substantially concurrently receive rowcommand information and column command information as part of anexchange with an external device.
 13. The memory device of claim 12,wherein the row command information and column command informationreceived as part of the exchange correspond to different write or readtransactions.
 14. The memory device of claim 13, where the differentwrite or read transactions are directed to different portions of the atleast two electrically isolated portions.
 15. A memory device,comprising: at least two electrically isolated memory portions, eachportion including banks of memory and circuitry to write and read datato the respective bank in association with memory write and readtransactions; interface circuitry to receive commands and to exchangethe write and read data external to the apparatus in association withthe memory write and read transactions; and logic to identify based onthe commands one of the at least two electrically isolated portions thatis the target of each transaction of the memory write and readtransactions, and to route said each write and read transaction to saidtarget; wherein the memory device is to receive serialized packetscomprising command information for each transaction, and each exchangeof command information with an external device comprises a portionindication and memory address information.
 16. The memory device ofclaim 15, wherein: each of the banks comprise dynamic random accessmemory (DRAM) cells; the memory device is characterized as having notiming constraint imposed on when a first portion of the at least twoelectrically isolated portions can be accessed relative to a secondportion of the at least two electrically isolated portions; and eachgiven portion of the at least two electrically isolated portion ischaracterized by a timing constraint, Trr, that must elapse between rowactivations within the given portion.
 17. The memory device of claim 15,wherein each given portion of the at least two electrically isolatedportions is isolated in a manner that sense amplifier activation for abank in the given portion does not corrupt concurrent data access inanother portion of the at least two electrically isolated portions. 18.A memory device, comprising: at least two electrically isolated memoryportions, each portion including banks of memory and circuitry to writeand read data to the respective bank in association with memory writeand read transactions; interface circuitry to receive commands andexchange the write and read data external to the apparatus inassociation with the memory write and read transactions, whereincommands for each transaction of the memory write and read transactionscomprise a portion indication, row control information and columncontrol information, received in a manner not separated by idle timeconsisting of one or more clock cycles; and logic to identify based onthe commands one of the at least two electrically isolated portions thatis the target of each transaction of the memory write and readtransactions, and to route said each write and read transaction to saidtarget.
 19. The memory device of claim 18, wherein the memory device isto receive the commands for each transaction in the form of serializedpackets from an external device.
 20. The memory device of claim 18,wherein: each of the banks comprise dynamic random access memory (DRAM)cells; the memory device is characterized as having no timing constraintimposed on when a first portion of the at least two electricallyisolated portions can be accessed relative to a second portion of the atleast two electrically isolated portions; and each given portion of theat least two electrically isolated portions is characterized by a timingconstraint, Trr, that must elapse between row activations within thegiven portion.
 21. The memory device of claim 18, wherein the memorydevice is to receive the commands via plural communication linksexternal to the memory device.